G.J. Cowle

High performance single frequency fiber grating-based erbium/ytterbium-codoped fiber lasers

The device characteristics of Er/sup 3+/,Yb/sup 3+/ single frequency fiber lasers are reported. A 5-cm long 1550-nm distributed feedback fiber laser with 4 mW output power is shown to have excellent specifications in terms of optical linewidth, signal-to-noise ratio (SNR), relative intensity noise, side-mode suppression and polarization purity. For higher power applications, a 1.5 cm single frequency Er/sup 3+/,Yb/sup 3+/ grating-based fiber laser with 60 mW output power and a net efficiency of 12% is demonstrated.

Polarization characteristics of fiber DFB lasers related to sensing applications

An experimental and theoretical investigation of how the polarization mode competition and beat frequency of Er-doped fiber distributed-feedback lasers depend on perturbations such as localized transverse forces, back reflections, or changes in pump polarization is reported. Good agreement between the experiments and a comprehensive theoretical model is obtained. Use of a dual-polarization laser as a transverse force sensor with a resolution on the order of 1-100 nN//spl radic/Hz above 20 Hz is also discussed.

Modelling of multi-line Brillouin/erbium fibre lasers

Laser sources with unique properties can be produced using a combination of nonlinear Brillouin gain in single-mode optical fibre (SMOF) and gain in erbium-doped fibre (EDF). Narrow bandwidth nonlinear gain from stimulated Brillouin scattering in SMOF determines the wavelength of operation, and gain in EDF allows efficient operation and large power extraction. Various cascading schemes based on the Brillouin/erbium fibre laser (BEFL) as well as distinctive multi-wavelength versions of the BEFL were proposed, being able to produce 10GHz combs of over 30 lines at 1550 nm. These multi-wavelength sources may be of use in future dense wavelength-division multiplexing systems. We explore fundamental aspects of BEFLs configured to generate multiple wavelengths with particular focus on the effects of the Brillouin and EDF pumps on the number of lines and the relationship between the intensities of the individual lines in the comb.

Characterization of special fibers and fiber devices

Methods for characterizing birefringent fibers (both those with high circular or linear birefringence and those with negligible intrinsic birefringence) are presented, and their relative merits are discussed. Fibers with high nonlinear coefficients exhibit interesting optical phenomena, and methods are developed to determine second harmonic, Pockels and Kerr effects, parametric phenomena, and the Verdet constant of silica and higher-loss, nonsilica fibers. Fibers containing rare-earth ions are of interest both as active (laser and amplifiers) and passive systems. Techniques are developed to characterize these devices, and conventional methods are modified to quantify dopant parameters within the fiber. Techniques for the measurement of the diverse properties of all these different fibers are presented with results, and, where appropriate, the problems with their characterization are discussed. >

Multiwavelength operation of Brillouin/erbium fiber lasers with injection-locked seeding

Brillouin/erbium doped fiber lasers (BEFLs) have recently been demonstrated as a novel mode of operation of fiber lasers, using both the gain of an erbium-doped fiber (EDF) and Brillouin gain in single-mode optical fiber. BEFLs can be configured to produce laser combs, with potential applications in dense wavelength-division multiplexing. In this paper we present a different regime of operation of a BEFL, in which a signal is injection locked in a ring resonator, which then seeds the BEFL modes.

Characterization of Site Dependent Pumping in EDFA

Site Dependent Pumping in EDFA has similar nature to Spectral Hole Burning effect, thus similar approach for characterization and modeling can be used. The wavelength selective effect on gain can reach several dB in EDFA.

Stable multiple wavelength generation in all-fibre DFB lasers

Fibre DFB lasers exhibit many attractive features and being based on and around a fibre Bragg grating they exhibit the robustness in performance offered by these, together with inherent fibre compatibility They can readily be manufactured to operate in both a single longitudinal and single polarisation mode and strong preferential output has also been demonstrated by offsetting the phase-shift from the centre position. As the technology of fibre Bragg grating fabrication and manipulation have reached a level where the formation of complex refractive index profiles are possible, the step towards all-fibre systems is approaching at rapid pace. Multiple wavelength laser configurations have been demonstrated and applications of these to, for example accurate frequency referencing in wavelength division multiplexed (WDM) systems has been proposed. Some of the previous demonstrations have suffered from the necessity to reduce the homogeneous linewidth to allow stable, multiple wavelength operation. In this paper we demonstrate multiple wavelength Moire DFB fibre lasers operating CW at room temperature on two wavelength channels separated by 25, 50 and 100 GHz respectively The output power from each wavelength channel is ~0 dBm for ~60 mW pump power 980 nm.

Optical fiber sources, amplifiers, and special fibers for application in multiplexed and distributed sensor systems

The paper describes how active fiber devices and special fibers can enhance the performance of multiplexed and distributed sensing systems. The use of active fibers, such as rare-earth-doped types, can act as powerful CW or pulsed sources, as wavelength-tunable sources, high-power amplifiers and as low-noise detector preamplifiers. Thus many arrangements for sensor-multiplexing, or distributed sensing, which may appear unattractively lossy on first consideration, may become perfectly viable with the insertion of active devices. The paper also reviews possible applications of special fibers in multiplexed and distributed sensors. The use of such fibers can greatly enhance the performance of sensor systems and even allow the construction of new types of optical sensor which were not previously possible with conventional fibers.

Noise characteristics of rare-earth-doped fiber sources and amplifiers

The A. M. and F. M. noise mechanisms in a number of rare-earth doped fiber devices are reviewed. Spontaneous emission noise presents an ultimate limit to the performance of a number of fiber laser and amplifier devices and the paper concentrates primarily on this area. Important concepts are reviewed and experimental and theoretical data are presented.

Narrow linewidth fiber laser sources

Laser sources based on rare-earth-doped single-mode optical fibres offer considerable potential as narrow-linewidth sources. Fibre laser sources have the capacity to produce highly-coherent low-noise output pumped by laser diodes. Fibre lasers are inherently compatible with optical fibres for transmission and sensing applications. Techniques for producing narrow-linewidth and single-longitudinal-mode operation in fibre lasers are reviewed.